Stump grinder with laterally offset grinding arm operated by single joystick

ABSTRACT

A stump grinder has a grinding arm that durably mounts a rotatable grinding wheel by securing the drive shaft of a motor to the grinding wheel such that a pair of bearings within the motor support one side of the grinding wheel and by supporting the other side of the grinding wheel with a stub shaft received within a third bearing. The grinding arm is laterally offset on the frame of the stump grinder to have a swing angle that is not symmetrical relative to the width of the frame, but with the swing angle starting at one side of the frame and then traversing across substantially the entire width of the frame to improve the ability of the operator to see the grinding wheel. A single joystick is movable in orthogonal directions corresponding to desired up and down and side-to-side pivoting motions of the grinding arm. The joystick includes a depressible trigger for starting and stopping the operation of the grinding wheel.

TECHNICAL FIELD

This invention relates generally to the field of stump grinding in whicha powered grinding wheel is used to grind or comminute a stump or otherwood debris into a pile of wood chips or particles.

BACKGROUND OF THE INVENTION

Stump grinders are well known devices that employ a pivotal grinding armthat carries a rotatable grinding wheel at its outer end. The grindingwheel extends generally vertically and has powered rotation about asubstantially horizontal axis of rotation. The pivotal grinding arm ispivotal on a support frame in an up and down motion about asubstantially horizontal axis. In addition, the grinding arm is alsopivotal in a side-to-side motion about a substantially vertical axis inmany stump grinders.

When the grinding wheel is placed into operation and is rotating in avertical plane about its substantially horizontal axis of rotation, theoperator can pivot the grinding arm up and down and from side-to-side.This causes the grinding wheel to bite into and traverse over the stumpor other wood debris that is to be grinded into particles. As repeatedpasses of the grinding arm and grinding wheel are made relative to thestump or other wood debris, the action of the grinding wheel graduallyreduces the stump or wood debris to small wood chips or fine particles.

Stump grinders typically have the pivotal grinding arm and the grindingwheel arranged generally symmetrically with respect to the lateral widthof the frame of the stump grinder. Thus, for an operator who is standingbehind the frame or is carried on the frame on some type of seat oroperator's platform, the grinding arm is usually disposed in a homeposition that is centered on the stump grinder frame and extends awayfrom the operator in a straight fore-and-aft direction. The grinding armtraverses from side-to-side in generally equal arcs to either side ofthe home position. However, in this centered home position, the view ofthe operator with respect to the action of the grinding wheel on thestump or wood debris can be blocked or obstructed by the structure ofthe grinding arm itself. In other words, the operator may not be able toclearly see the contact area between the grinding wheel and the stump orwood debris.

In addition, the task of operating the stump grinder can involvemultiple controls that can be difficult or at least confusing for theoperator to use. There must be a set of traction and steering controlsfor the operator to use to control the forward and reverse motion of thestump grinder frame and to steer or turn the stump grinder frame. Inaddition, there must be other grinding arm controls to allow theoperator to manipulate the grinding arm to cause the grinding arm topivot up and down and to traverse from side-to-side out of the centeredhome position. There must also be an on-off grinding control to start orstop the rotation of the grinding wheel on the grinding arm.

Typically, the grinding arm controls often take the form of multiplelevers. One lever controls the up and down motion of the grinding arm.Another lever controls the side-to-side traverse. The on-off grindingcontrol often comprises yet another separate control, i.e. a separateon-off switch. Needless to say, it is not an easy task for the operator,particularly an unskilled operator who might rent a stump grinder from arental business and is thus somewhat unfamiliar with the controls, tocoordinate and properly use all of the multiple controls typically foundon a stump grinder.

Finally, it should be apparent that the grinding wheel of a stumpgrinder should be reliably and durably driven in a cost-effective andsimple manner. Mechanical drive systems, such as belt or chain drives,are prone to breaking given the forces involved in stump grinding andare costly and time consuming to maintain and to keep properly adjusted.Hydraulic motors carried on the grinding arm have been used to directlydrive or rotate the grinding wheel without the interposition of belt orchain drives. However, the high forces involved in grinding that aretransmitted to the shaft of such a hydraulic motor often exert largeloads on the motor, leading to premature wear and failure of the motor.Given the relatively high cost of such hydraulic motors, this is adisadvantage of known designs in which hydraulic motors have been usedto directly drive the grinding wheels.

SUMMARY OF THE INVENTION

One aspect of this invention relates to a stump grinder which comprisesa frame that is supported for movement over the ground, the frame havinga width between a left side and a right side thereof. A rotatablegrinding wheel rotates about a substantially horizontal wheel axis forgrinding or comminuting stumps or wood debris. A grinding arm comprisesa rear section that is pivotally journalled to the frame for up and downpivoting about a substantially horizontal pivot axis, the rear sectionof the grinding arm being located substantially proximate to and alongone side of the frame such that the rear section of the grinding arm islaterally offset relative to the frame. The grinding arm also has afront section that carries the rotatable grinding wheel. The frontsection is pivotally journalled to the rear section of the grinding armfor side-to-side pivoting about a substantially vertical pivot axis. Thefront section of the grinding arm has a position in which the frontsection of the grinding arm is longitudinally aligned in a fore-and-aftdirection with the rear section of the grinding arm to be located withthe rear section substantially proximate to and along the one side ofthe frame. The front section is pivotal about the vertical pivot axisout of the aligned position to traverse in a sideways direction across asubstantial portion of the entire width of the frame with the rearsection of the grinding arm remaining in place substantially proximateto and along the one side of the frame to allow the operator to betterview, in a manner that is unobstructed by the rear section, theoperation of the grinding wheel carried on the front section of thegrinding arm.

Another aspect of this invention relates to a stump grinder whichcomprises a frame that is supported for movement over the ground. Arotatable grinding wheel rotates about a substantially horizontal wheelaxis for grinding or comminuting stumps or wood debris. A grinding armis movable relative to the frame with the grinding arm mounting thegrinding wheel. The grinding arm has a pair of spaced side walls betweenwhich the grinding wheel is rotatably journalled. A motor is secured toone side wall of the grinding arm, the motor having a drive shaft thatextends inwardly and that has a drive connection to the grinding wheelsuch that rotation of the drive shaft of the motor rotates the grindingwheel about the horizontal axis of rotation thereof. The motor has apair of radial bearings for directly supporting the drive shaft of themotor and thus for indirectly supporting the grinding wheel from oneside of the grinding wheel. A stub shaft is operatively secured to anopposite face of the grinding wheel. A third radial bearing is securedto an opposite side wall of the grinding arm for receiving the stubshaft, the stub shaft and third bearing additionally supporting thegrinding wheel from an opposite side of the grinding wheel.

Yet another aspect of this invention relates to a stump grinder whichcomprises a frame that is supported for movement over the ground. Arotatable grinding wheel is provided that rotates about a substantiallyhorizontal wheel axis for grinding or comminuting stumps or wood debris.A grinding arm is movable relative to the frame and mounts the grindingwheel. The grinding arm is pivotal about substantially horizontal andvertical axes to cause the grinding arm to pivot up and down about thehorizontal axis and from side-to-side about the vertical axis. A singlejoystick controls the up and down and side-to-side pivoting of thegrinding arm. The joystick is carried on the frame for manipulation byan operator along first and second orthogonal axes that are correlatedto desired directions of pivoting of the grinding arm, the joystickbeing pulled rearwardly out of a neutral position in a fore-and-aftdirection to lift the grinding arm, being pushed forwardly out of aneutral position in a fore-and-aft direction to lower the grinding arm,being pulled to the right out of a neutral position in a side-to-sidedirection to swing the grinding arm to the right, and being pulled tothe left out of a neutral position in a side-to-side direction to swingthe grinding arm to the left.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described more completely in the followingDetailed Description, when taken in conjunction with the followingdrawings, in which like reference numerals refer to like elementsthroughout.

FIG. 1 is a perspective view of a stump grinder according to thisinvention;

FIG. 2 is a top plan view of the stump grinder of FIG. 1;

FIG. 3 is a partial perspective view of the stump grinder of FIG. 1,particularly illustrating the left side of the forwardly extendinggrinding arm;

FIG. 4 is a perspective view similar to FIG. 3, but illustrating theright side of the forwardly extending grinding arm;

FIG. 5 is a perspective view of the front of the grinding arm of thestump grinder of FIG. 1, particularly illustrating the third bearing anddrive motor that support the grinding wheel from opposite sides thereof;

FIG. 6 is a perspective view similar to FIG. 5, but with the thirdbearing, stub shaft support hub, drive hub and drive motor for thegrinding wheel being shown in exploded form for the sake of clarity; and

FIG. 7 is a partial perspective view of the stump grinder of FIG. 1,particularly illustrating the single joystick control for operating thegrinding arm and the grinding wheel.

DETAILED DESCRIPTION

Referring first to FIG. 1, one embodiment of a stump grinder accordingto this invention is generally illustrated as 2. Stump grinder 2comprises a traction frame 4 that carries a power source 6, such as aninternal combustion engine, that provides the power for propelling frame4 over the ground. The propulsion means can take different forms, but inthe illustrative embodiment shown in FIG. 1 comprises a pair ofelongated, ground engaging tracks 8. A single such track 8 is locatedadjacent and immediately outboard of each of the opposite left and rightsides of frame 4.

Frame 4 has an upwardly extending portion 10 at the rear thereof behindwhich an operator may walk on the ground as frame 4 is propelled overthe ground. The top of rear portion 10 of frame 4 carries variouscontrols that may be comfortably gripped by the operator as the operatorstands behind frame 4. Among these controls is a traction and steeringcontrol indicated generally as 12. When power source 6 is in operation,the operator may manipulate traction and steering control 12 to cause adrive system (not shown) carried on frame 4 to drive ground engagingtracks 8 in forward or reverse at desired speeds with steering beingaccomplished through driving tracks 8 differentially at differentspeeds. The tracked frame 4 illustrated herein as well as the tractionand steering control 12 are of the type shown in U.S. Pat. Nos.6,460,640 and 6,709,223, which are assigned to the assignee of thisinvention and which are hereby incorporated by reference.

A grinding arm 14 is mounted on the front of frame 4 in a laterallyoffset position in which grinding arm 14 extends forwardly along theleft side of frame 4 with grinding arm 14 overlying the left side offrame 4. Grinding arm 14 comprises two sections thereof, namely a rearsection 16 and a front section 18. Rear section 16 of grinding arm 14pivots on frame 4 about a lateral, substantially horizontal pivot axis xsuch that the entire grinding arm 14, i.e. both the rear and frontsections 16 and 18 thereof, can swing or pitch downwardly or upwardlytowards or away from the ground as indicated by the arrows A and B inFIG. 3. Pivot axis x is located very low on frame 4 at a distance thatis only a few inches above the rotational axis of the front drive pulleyor sprocket on track 8. Front section 18 of grinding arm 14 pivotsrelative to rear section 16 about a substantially vertical pivot axis yto swing or pivot front section 18 from side-to-side as indicated by thearrows C and D in FIGS. 2 and 3.

Referring to FIGS. 3 and 4, frame 4 includes a pair of laterally spaced,forwardly extending support walls 20 having at least lower portionsthereof that extend forwardly to a front end of frame 4. A top wall 22joins and connects support walls 20 together over rear portions ofsupport walls 20. Note that in FIG. 4 the inner support wall 20 has beenremoved to illustrate a first hydraulic actuator 24 that is locatedbetween support walls 20 and beneath top wall 22. The cylinder 26 offirst hydraulic actuator 24 is pivotally connected to the rear ofsupport walls 20 by a pivot pin 30.

Rear section 16 of grinding arm 14 also includes a pair of side walls 32that are joined or connected together by a top wall 34. Side walls 32 ofrear section 16 have a slightly narrower spacing than the spacing ofsupport walls 20 of frame 4 such that rear ends of side walls 32 of rearsection 16 nest between support walls 20 of frame 4. Side walls 32 ofrear section 16 are generally L-shaped with one leg of the L-shapeextending downwardly to pivotally journal rear section 16 of grindingarm 14, and thus the entire grinding arm 14, on a pivot pin 36 that iscarried between support walls 20 and that forms the horizontal pivotaxis x for grinding arm 14. The rod 27 of first hydraulic actuator 24pivotally connects to the rear ends of side walls 32 of rear section 16at a pivot pin 38 close to the juncture of the legs of the L-shape andabove the pivot pin 36 forming the pivot axis x. Thus, retraction of rod27 into cylinder 26 of first hydraulic actuator 24 causes upwardpivoting of grinding arm 14 in the direction of arrow B and extension ofrod 27 out of cylinder 26 causes downward pivoting of grinding arm 14 inthe direction of arrow A.

Front section 18 of grinding arm 14 is generally similar in structure tothat of rear section 16 in the sense that front section 18 alsocomprises a pair of laterally spaced side walls 40 that are joined orconnected together by a top wall 42. Side walls 40 of front section 18are laterally spaced apart by a greater distance than side walls 32 ofrear section 16 to allow the rear of front section 18 to telescopicallynest over and around the front of rear section 16. A vertical pivotstructure 44 forming the vertical pivot axis y pivotally joins the frontand rear sections 18 and 16 together with side walls 40 of front section18 having U-shaped cutouts 46 to allow front section 18 to swing orpivot around the front of rear section 16 without interference betweenthe two.

As shown in FIG. 3, a second hydraulic actuator 48 has a cylinder 50that is pivotally mounted by a pivot pin 52 to the exterior of one ofside walls 32 of rear section 16. Rod 51 of second hydraulic actuator 48is pivotally connected to an exterior of one of side walls 40 of frontsection 18 of grinding arm 14. Extension and retraction of rod 51 ofsecond hydraulic actuator 48 causes front section 18 of grinding arm 14to swing or pivot about the vertical pivot axis y relative to rearsection 16 of grinding arm 14.

FIGS. 1-4 illustrate grinding arm 14 in a home position in whichgrinding arm 14 is substantially horizontal and with grinding arm 14being longitudinally aligned with rear section 16 of grinding arm 14with grinding arm 14 extending straight ahead in a longitudinalfore-and-aft direction. From this home position, grinding arm 14 canpivot or pitch downwardly in the direction of arrow A in FIG. 3approximately 28° and can pivot or pitch upwardly in the direction ofarrow B in FIG. 3 approximately 52°, for a total of approximately 80° ofswing about the horizontal pivot axis x. From this home position, frontsection 18 of grinding arm 14 can pivot to the left in the direction ofarrow C in FIG. 3 approximately 80° and can pivot to the right in thedirection of arrow D in FIG. 3 approximately 20°, for a total ofapproximately 100° of swing about the vertical pivot axis y. Clearly,front section 18 of grinding arm 14 has an asymmetric swing angle inwhich it swings approximately four times further to the right than itdoes to the left (i.e. 80° to the right versus 20° to the left).

Front section 18 of grinding arm 14 has a front end that houses arotatable grinding wheel 54. Grinding wheel 54 is in the form of asubstantially flat, planar disc that has a plurality of stump or woodgrinding tools 56 attached to the periphery thereof at circumferentiallyspaced locations. The nature of the wood grinding tools 56 that are usedis not important to this invention and may be of any type that is knownin the stump grinder art. Grinding wheel 54 is rotatably journalled ongrinding arm 14 for rotation about a lateral, substantially horizontal,grinding axis x1. See FIG. 3.

As shown in FIGS. 5 and 6, grinding wheel 54 is mounted to front section18 of grinding arm 14 and is powered by a hydraulic motor 58 in a simpleand durable manner. Motor 58 is bolted to an exterior of one of sidewalls 40 of front section 18. Motor 58 has an inner portion 60 extendingthrough side wall 40 to be positioned relatively close to one side faceof grinding wheel 54. Motor 58 has an inwardly projecting drive shaft 62that sticks further inwardly from the inner portion of motor 58 suchthat drive shaft 62 extends into, but not through, a central bore 64 ingrinding wheel 54. FIG. 6 depicts central bore 64. Motor 58 includes apair of radial bearings (not shown) within the housing thereof thatrotatably journal and support drive shaft 62 of motor 58 against radialloads on drive shaft 62. Motor 58 is preferably a TJ Series Motormanufactured by the Hydraulic Pump/Motor Division of Parker HannifinCorporation.

One face of grinding wheel 54 has a drive hub 68 bolted thereto. Theinterior of drive hub 68 has a keyed, splined, or tapered driveconnection (not shown) to drive shaft 62 of motor 58. Thus, as motor 58is rotated by hydraulic fluid flow therethrough, the rotation of driveshaft 62 will be transferred through drive hub 58 to grinding wheel 54to rotate the same about its axis of rotation x1. The support ofgrinding wheel 54 could end there, as is conventional in the stumpgrinder art, with grinding wheel 54 simply being supported by motor 58alone. However, the Applicants have found that this imposes undesirablyhigh loads on motor 58 in many stump and wood grinding operations.

Thus, grinding wheel 54 of this invention is further supported on theother side or face thereof as well. A support hub 70 that carries anoutwardly extending stub shaft 72 is bolted to the opposite side face ofgrinding wheel 54. See FIG. 7. A third radial bearing 74, namely a stubshaft bearing, is then bolted to the inside of the opposite side wall 40of front section 18 of grinding arm 14. Third bearing 74 rotatablyjournals and supports stub shaft 72 to support the opposite side ofgrinding wheel 54. Thus, going from right to left in FIG. 5, there arethree radial bearings that carry the radial loads from grinding wheel54, i.e. a first drive shaft radial bearing inside motor 58, a seconddrive shaft radial bearing inside motor 58 with both drive shaftbearings being on one side of grinding wheel 54, and a third stub shaftradial bearing 74 on the opposite side of grinding wheel 54. This allowsa hydraulic motor 58 to be simply and inexpensively bolted to one sidewall 40 of front section 18 of grinding arm 14 but, with the use of stubshaft bearing 74, still provides radial bearing support on both sides ofgrinding wheel 54. Enough vertical slop or play is desirably providedbetween the bolts 76 and the holes that are used to bolt stub shaftbearing 74 in place such that the vertical position of stub shaftbearing 74 on side wall 40 can be shifted up and down as need be beforestub shaft bearing 74 is firmly tightened into place to allow alignmentof stub shaft 72 with drive shaft 62.

Referring now to FIGS. 2 and 7, stump grinder 2 of this inventionincludes a joystick 80 for simple and intuitive operation of grindingarm 14 and grinding wheel 54. Joystick 80 has a centered neutralposition as is typical of joysticks, which neutral joystick positioncorresponds to the home position of grinding arm 14. Joystick 80 ispivotally mounted in any suitable manner in frame 4 for movement in alongitudinal fore-and-aft direction as indicated by the arrows E and Fin FIG. 2. This longitudinal motion of joystick 80 will control firsthydraulic actuator 24 to cause grinding arm 14 to pivot up in thedirection of the arrow B when joystick 80 is pulled back in thedirection of arrow F and to cause grinding arm 14 to pivot down in thedirection of the arrow A when joystick 80 is pushed forwardly in thedirection of arrow E. The pivotal mounting of joystick 80 also permitsmovement of joystick 80 in a lateral side-to-side direction as indicatedby the arrows G and H in FIG. 2. This lateral motion of joystick 80 willcontrol second hydraulic actuator 48 to cause front section 18 ofgrinding arm 14 to swing from side-to-side in a direction correspondingto the direction of joystick 80, front section 18 swinging in thedirection of the arrow C when joystick 80 swings in the direction of thearrow G and in the direction of the arrow D when joystick 80 swings inthe direction of the arrow H.

Thus, the user need only operate a single control, namely joystick 80,and need move that control only in a direction corresponding to the upand down and side-to-side pivoting that is desired for grinding arm 14.This greatly eases the task of operating grinding arm 14, especially fora new or relatively unskilled operator, since the operator need not gripand coordinate the operation of separate control levers. All theoperator need use is the single joystick 80.

To further ease the task of operating stump grinder 2, joystick 80 canbe provided with a compressible trigger 82 on the front side thereofthat controls the on-off operation of grinding wheel 54. In order tostart grinding wheel 54, the operator need only press a button 84 on topof joystick 80 and then squeeze trigger 82 rearwardly until the top oftrigger 82 abuts against joystick 80. A switch (not shown) will beclosed by trigger 82 and grinding wheel 54 will start rotating. Oncetrigger 82 is closed, the operator can release button 84 on top ofjoystick 80. To stop grinding wheel 54, the operator need only releasetrigger 82, which causes trigger 82 to pivot back forwardly away fromjoystick 80 under the bias of a spring (not shown), to stop the rotationof grinding wheel 54. Integrating the on-off control for grinding wheel54 on the same joystick 80 that controls the up and down pitching ofgrinding arm 14 and the side-to-side traverse of grinding wheel 54further simplifies the task of operating stump grinder 2.

The offset nature of grinding arm 14 provides better visibility to theoperator during a stump grinding operation. Of course, during such anoperation, the operator will wear eye protection to protect his or hereyes from wood chips or other debris being generated by stump grinder 2.But, grinding wheel 54 can now traverse or swing from the extreme leftside of frame 4 in a large arc extending in front of frame 4 and acrosssubstantially the entire width of frame 4 without being obstructed byrear section 16 of grinding arm 14, which remains in place on the leftside of frame 4 out of the line of vision of the operator. This allowsthe operator to better see and place grinding wheel 54 at a desiredlocation on the stump or other debris that is being ground down.

Various modifications of this invention will be apparent to thoseskilled in the art. Thus, the scope of this invention is to be limitedonly by the appended claims.

The invention claimed is:
 1. A stump grinder, which comprises: (a) aframe that is supported for movement over the ground; (b) a rotatablegrinding wheel that rotates about a substantially horizontal axis forgrinding or comminuting a stump; (c) a grinding arm that is movablerelative to the frame and that mounts the grinding wheel, wherein thegrinding arm is pivotal about substantially horizontal and vertical axesto cause the grinding arm to pivot up and down about the horizontal axisand from side-to-side about the vertical axis; (d) a single joystick forcontrolling the up and down and side-to-side pivoting of the grindingarm when the grinding wheel is rotating and contacts the stump duringthe stump grinding operation, wherein the joystick is carried on theframe for manipulation by an operator along first and second orthogonalaxes that are correlated to desired directions of pivoting of thegrinding arm, wherein the joystick is pulled rearwardly out of a neutralposition in a fore-and-aft direction to lift the grinding arm and therotating grinding wheel carried thereon higher on the stump or out ofcontact with the stump, wherein the joystick is pushed forwardly out ofa neutral position in a fore-and-aft direction to lower the grinding armand the rotating grinding wheel carried thereon into contact with thestump or lower on the stump, wherein the joystick is pulled to the rightout of a neutral position in a side-to-side direction to swing thegrinding arm and the rotating grinding wheel carried thereon to theright as the rotating grinding wheel contacts the stump, and wherein thejoystick is pulled to the left out of a neutral position in aside-to-side direction to swing the grinding arm and the rotatinggrinding wheel carried thereon to the left as the rotating grindingwheel contacts the stump; and (e) wherein the joystick has at least onecontrol to start or stop the rotation of the grinding wheel to begin orend a stump grinding operation.
 2. The stump grinder of claim 1, whereinthe at least one control comprises a depressible trigger that can besqueezed against the joystick to start the rotation of the grindingwheel, and wherein the rotation of the grinding wheel is stopped whenthe trigger is released.
 3. The stump grinder of claim 2, wherein thejoystick further has a depressible button that must be pressed beforethe depressible trigger is squeezed against the joystick in order tostart the rotation of the grinding wheel.
 4. The stump grinder of claim3, wherein the button is configured to be released after the grindingwheel has started its rotation without such release stopping therotation of the grinding wheel for so long as the depressible triggerremains squeezed against the joystick.